Same problem w/ visual editor after upgrade to 3.8.1, but only in Firefox, not in Chrome. Found out it was because the visual editor needs Java/Javascript, and my FF add-on of QuickJava had toggled off J/JS when I did the upgrade. Why? God knows! When I switched J/JS back on, visual editor worked fine. Found that only after trying all of the above steps.
Maybe this will help someone…